EGG-LAYING in vitro by Schistosoma japonicum and S. mansoni in serum media was not described by early investigators1–4, and presumably did not occur. Later it was reported that a few eggs were laid when flukes were kept for up to two months in a glass apparatus with provision for daily change of medium (horse serum)5. A method of maintaining S. mansoni flukes so that a regular output of 30–40 eggs a day was obtained has recently been published6–8. Some cell division was seen, but the eggs did not mature in serum media, saline or Tyrode's solution.